The central gustatory neuraxis has a centrifugal component arising from forebrain regions associated with the motivational or appetitive aspects of feeding. The function of this descending pathway is unknown, but similar pathways in other systems are thought to filter or modulate ascending sensory information. Therefore, the orosensory centrifugal pathway may also be designed to modulate the quality of afferent gustatory information at the brainstem level based on appetitive processing of orosensory, post-ingestional and/or post-adsorptive gastrointestinal signals in the ventral forebrain. This circuitry would influence how orosensory information modulates eating behavior, acting to prevent ingestion of potential poisons and to ensure ingestion of a proper balance of foodstuffs. Elucidating the functional neural circuitry of the control of feeding is the long term goal of the proposed research. The specific aim of the proposed experiments is to describe the anatomical organization of the descending pathway from two forebrain regions, the lateral hypothalamus and central nucleus of the amygdala to the orosensory brainstem, as little is known about the anatomy of the circuitry, let alone the function of the descending pathway(s). Neuroanatomical techniques will be used to determine the specificity of the descending input onto functional subdivisions of the rostral nucleus of the solitary tract (NST) and parabrachial nucleus (PBN). The descending terminal fields will also be related to the locations of orosensory-related ascending NST and PBN efferent neurons within the same preparation. Immunohistochemical techniques will also be used to determine if the descending pathway uses gamma-aminobutyric acid (GABA) or substance P. There is indirect evidence that these two neurochemicals are utilized by the descending orosensory- related circuitry. Knowledge of the underlying anatomical design of the circuitry is a necessary step leading to an understanding of the functional link between the forebrain and orosensory input arising from ingestion. These descending circuits may be the neural basis for such phenomena as illness-related anorexia, conditioned taste aversions and sensory specific satiety (postingestive alliesthesia), and may be involved in the underlying mechanisms of central neuroregulatory imbalances, like those associated with human appetitive disorders (e.g., obesity, anorexia and bulimia nervosa).